Efficacy of two and three-spray programmes with new strobilurin fungicides in winter wheat

Summary

Sector:
Cereals & Oilseeds
Project code:
PR391
Date:
01 April 2002 - 31 March 2005
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£47,328 from HGCA (Project No. 2669)
Project leader:
M Self The Arable Group, Morley St Botolph, Wymondham, Norfolk NR18 9DB

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About this project

Abstract

Fungicide programmes were compared in two experiments a year for three years, one in a susceptible variety to Septoria tritici (Consort) and one in a less susceptible variety to S. tritici (Deben) at Manor Farm, Morley St Botolph, Norfolk on a sandy loam soil.  In all three seasons S. tritici was the predominant foliar disease.  The occurrence of the mutation in isolates that confer resistance of S. tritici to strobilurins increased rapidly during the period when the experiments were carried out, from a relatively low level at the beginning of the 2002 growing season to a very high level at the end of the 2004 growing season.  Due to the changing background of fungicide resistance, the conclusions drawn reflect only the individual years and the location in which the experiments were done:

  • Cultivars susceptible to S. tritici required a three-spray programme to provide a reliable and economic level of disease control.  Changes in resistance to the strobilurins over the time period of the project may have influenced the number of sprays required in the less susceptible variety.
  • In less disease susceptible varieties in particular, there was some flexibility in the timing of the second fungicide application (T2 - typically at full flag leaf emergence) within a two or three-spray programme.  The degree of flexibility was governed by the dose of fungicides at the first application (T1 - typically at final leaf three emergence). Disease pressure late in the season and fungicide dose also appeared to be influenced by the level of resistance to the strobilurins.
  • There was a possible advantage in delaying T2 to early ear emergence where it contained a strobilurin, even when a third fungicide application (T3 - typically at mid-anthesis) not containing a strobilurin was applied.  This was recorded in Consort in 2002, despite a slight reduction in disease control, when resistance to the strobilurins was not of great significance but did not occur in 2003, when resistance was more significant.  However, it was still recorded in Deben in 2003 (there was insufficient disease in Deben in 2004 to base any conclusion).
  • If T2 is delayed to ear emergence the benefit of a T3 application is not necessarily diminished and may be enhanced, particularly if the T3 is strobilurin based and the T2 does not include a strobilurin.
  • With increasing resistance to strobilurins throughout the project the emphasis of their value appeared to change from S. tritici control and ear disease control plus some "physiological" benefits to ear disease control and "physiological" benefits.  This suggests that if there is a role for strobilurins on future wheat crops they should be applied at the later timings within the fungicide strategy, particularly at T3.
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